Hitting moving targets: Co-operative control of 'when' and 'where'

In this study we present evidence that two independent regulatory mechanisms, governing when and where the target will be hit, function together to allow us to hit moving targets. In the first part of the paper we show that subjects anticipate that the targets will have moved by the time they reach them, but that they do not anticipate how far they will have moved. The resulting systematic errors are largely made up for by continuously adjusting the movement of the hand as the estimate of the position at which the target will be hit improves. The estimate improves during the movement because the time for which motion is predicted, rather than perceived, decreases as we get closer to the moment of the hit. In the second part we argue that part of the errors cannot be accounted for by continuously adjusting the movement of the hand, due to the time it takes for visual information to be transformed into muscle contractions. These errors are compensated for by moving the hand more quickly towards fast targets.